In semiconductor technologies, image sensors include a plurality of sensor elements, or pixels, formed in a semiconductor substrate. The sensor elements are used for sensing a volume of exposed light projected towards the semiconductor substrate. The sensor elements can be formed on the front side of the substrate and light can be projected towards the front side or the backside of the substrate to reach the sensors. However, light targeted for one sensor element (and the electrical signal induced thereby) may spread to other sensor elements, which causes crosstalk. Improvements of the image sensors and/or the corresponding substrate are desired.